1. Field of the Invention
This invention relates to a lighting device for illuminating a display surface provided on a display surface side, and an electronic provided with a non-light emitting display device illuminated by a front light.
2. Description of Prior Art
A non-light emitting display device such as a liquid crystal display device which consumes less power, is small-sized and thin is indispensable as display means for an electronic. A liquid crystal display device is categorized into a transmission type and a reflection type. The transmission type liquid crystal display device is provided with a back light for illuminating a display surface from behind arranged on a back side of the liquid crystal display device. The reflection type liquid crystal display device is provided with a front light for illuminating a display surface from the front arranged on a display surface side of the liquid crystal display device. The front light has an advantage to the back light in that it can illuminate by using external light and consumes less power, and thus a variety of front lights have been developed for commercial uses. (See JP 10-311915, A and JP 10-153777, A)
FIG. 6 illustrates one example of an electronic provided with a reflection type liquid crystal display device having a front light. The electronic includes a PDA such as a mobile computer, a portable telephone, and an electronic still camera or the like. A body of the electronic 61 houses a reflection type liquid crystal panel 62. A front light 63 is provided on a display surface side of the liquid crystal panel 62. The front light 63 comprises a line-shaped light source 64 such as a cold cathode fluorescent lamp, a light guide plate 65 for illuminating the display surface of the liquid crystal panel 62 by introducing light from the light source 64 and transmitting external light, and a reflection preventive film 66 attached on a back surface of the light guide plate 65 for improving visibility.
A surface opposite to a surface of the light guide plate 65 facing to the liquid crystal panel 62 includes a first inclining surface 67 inclining to a surface provided with the light source 64 and a second inclining surface 68 inclining to an opposite surface to the surface provided with the light source 64. The first and second inclining surfaces 67, 68 are formed. A peak line and a valley line formed by the first inclining surface 67 and the second inclining surface 68 are formed alternately and parallel with each other. When regarding a plane including the valley line as a virtual plane, an angle xcex2 of the first inclining surface 67 to the virtual plane is far greater than an angle xcex1 of the second inclining surface 68 (See FIG. 7). For example, the angle xcex2 of the first inclining surface 67 is approx. 40-43xc2x0, the angle xcex1 of the second inclining surface 68 is approx. 2-5xc2x0. A projected area of the first inclining surface 67 to the virtual plane is far smaller than the projected area of the second inclining surface 68 (for example, 1:10-30).
The light guide plate 65 becomes thinner as it is farther from a surface for introducing light from the light source 64, and has a cross section of a wedge shape. A back surface of the light guide plate 65 (on the liquid crystal panel side) for attaching the reflection preventive film 66 is approximately flat.
Such the electronic has the light source 64 arranged on an upper side of the light guide plate 65 with respect to upper and lower directions of the body 61. In watching the liquid crystal panel 62 by utilizing external light 70, the external light 70 is incident from the upper direction of the body 61 to the light guide plate 65 and transmits the light guide plate 65 so that the liquid crystal panel 62 is illuminated. A viewer perceives a display of the liquid crystal panel 62 by looking to a direction of the light guide plate 65 and observing reflective light from the liquid crystal panel 62 through the light guide plate 65.
However, when observing the liquid crystal panel 62 by utilizing external light, parallax may be generated on a part of the display to be observed. As shown in FIG. 7, when the external light incident from an upper part of the electronic body 61 is reflected to the liquid crystal panel 62 after transmitting through the light guide plate 65 and transmits the light guide plate 65 again, more than two reflective light of a single image are perceived at a certain visual angle because inclining angles of the first and second inclining surfaces 67, 68 are different. For example, the reflective light of an image perceived by a viewer which transmits the second inclining surface 68 at a point A is observed at a position shifted from the point A to S1, and the reflective light perceived by the viewer which transmits the first inclining surface 67 is observed at a position shifted from the point A to S2. Therefore the two images shifted by S1+S2 are observed and the viewer perceives parallax. Reflective light of a single image except for a certain visual angle does not cause parallax because the reflective light is not perceived simultaneously by the viewer.
When parallax caused by a front light (or a light guide plate) is generated in the display to be observed, the display quality of the reflection type liquid crystal display device provided with the front light is degraded, causing a problem in practical use.
This invention was made to provide an electronic provided with a reflection type liquid crystal display device having a front light of good display performance in practical use by suppressing parallax on a display to be observed. The invention also provides a lighting device capable of suppressing parallax on a display to be observed, and a light guide plate to be used for the lighting device.
An electronic provided with a non-light emitting display device according to this invention comprises non-light emitting display means and a lighting device for illuminating a display surface provided on a display surface side of the non-light emitting device. The lighting device comprises a light source and a light guide plate including an incident surface for introducing light from the light source, an emitting surface for emitting incident light, and an opposite surface for transmitting external light and reflecting light incident from the incident surface facing to the emitting surface. The opposite surface of the light guide plate includes a first inclining surface inclining to the incident surface and a second inclining surface inclining to an opposite surface to the incident surface which are alternately formed. A peak line and a valley line parallel to each other are formed by the first inclining surface and the second inclining surface, and the second inclining surface for forming the valley line with the first inclining surface is positioned in an upper direction of the body of the electronic.
As described above, the opposite surface of the light guide plate includes a plurality of the first inclining surfaces inclining to an incident surface side and facing to the incident surface, and a plurality of the second inclining surfaces inclining to an opposite surface side to the incident surface and facing to the opposite surface to the incident surface. The second inclining surface for forming the valley line with the first second inclined surface is formed so as to face to an upper direction of the body of the electronic, and parallax in a normal use of the electronic is prevented.
When regarding a plane including the valley line as a virtual plane, a projected area of the second inclining surface to the virtual plane is larger than a projected area of the first inclining surface to the virtual plane.
An angle of the first inclining surface to the virtual plane may be 45-90xc2x0 in this invention.
When regarding a plane including the valley line as a virtual plane, an angle of the first inclining surface to the virtual plane may be 45-90xc2x0, enabling the viewer to perceive sufficient illumination light quantity.
A light guide plate according to this invention is used for a lighting device for illuminating a display surface provided on a display surface side of a non-light emitting display device and comprises an incident surface for introducing light from a light source arranged by facing to the light source, an emitting surface for emitting incident light, and an opposite surface for reflecting the incident light from the incident surface and transmitting external light arranged oppositely to the emitting surface. The opposite surface includes a first inclining surface inclining to the incident surface and a second inclining surface inclining to an opposite surface to the incident surface which are alternately formed, a peak line and a valley line parallel to each other are formed by the first inclining surface and the second inclining surface. When regarding a plane including the valley line as a virtual plane, an projected area of the second inclining surface to the virtual plane is larger than a projected area of the first inclining surface to the virtual plane, and the first inclining surface has an angle of 45-90xc2x0 to the virtual plane.
With this structure, a light guide plate capable of supplying sufficient illumination light quantity is provided.
A lighting device according to this invention comprises a light guide plate and a light source provided on an incident surface side of the light guide plate. The light guide plate includes an incident surface for introducing light from the light source arranged by facing to the light source, an emitting surface for emitting incident light, and an opposite surface for reflecting the incident light from the incident surface and transmitting external light. The opposite surface includes a first inclining surface inclining to the incident surface and a second inclining surface inclining to an opposite surface to the incident surface which are alternately formed. A peak line and a valley line parallel to each other are formed by the first inclining surface and the second inclining surface. And when regarding a plane including the valley line as a virtual plane, a projected area of the second inclining surface to the virtual plane is larger than a projected area of the first inclining surface to the virtual plane, and the first inclining surface has an angle of 45-90xc2x0 to the virtual plane.
With the above structure, a bright display surface can be provided and a front light capable of illuminating sufficiently is provided.